Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Guarantees
Commercial letters of credit and SBLCs	$ 1,632,585	$ 1,655,897
Accrued expenses and other liabilities
Guarantees
Allowance for unfunded credit reserves	13,400	12,700
Other Commitments
Unfunded commitments in investments in qualified affordable housing partnerships, tax credit and other investments	162,600	169,200
Single Family and Multi-family Residential | Loans Sold or Securitized with Recourse
Guarantees
Principal amount outstanding on loans sold or securitized	108,700	113,700
Maximum potential future payments up to recourse component	37,800	38,700
Single Family and Multi-family Residential | Loans Sold or Securitized with Recourse | Accrued expenses and other liabilities
Guarantees
Allowance for unfunded credit reserves	200	$ 214
Standby Letters of Credit
Guarantees
Commercial letters of credit and SBLCs	1,570,000
Commercial Letters of Credit
Guarantees
Commercial letters of credit and SBLCs	$ 60,500